The present invention relates to methods for treating muscle injuries. In particular, the present invention relates to a method for treating an injured muscle by administration of a neurotoxin to the injured muscle.
Injuries to muscles include acute injuries to skeletal muscles such as contusions (bruises), lacerations, ischemia, strains, and complete ruptures. These injuries may cause tremendous pain and can incapacitate the affected person, preventing them from being able to go to work or even to participate in normal daily activities. Of the acute injuries to skeletal muscles, strain (also known as stretch-induced injuries) is most common. For example, strains can account for up to 30% of all injuries treated by occupational or sports medicine professionals. Garrett et al. Am J Sports Med, 24(6):S2-S8, 1996.
A muscle strain injury is characterized by a disruption of a muscle-tendon unit. The disruption of the muscle-tendon unit may occur anywhere on the muscle. This type of injury most commonly occurs near the myotendinous junction (MTJ) of the superficial muscles working across two joints, such as the rectus femoris, semitendinousus and gastroenemius muscles.
Muscle strain may result from an eccentric exercise, or uncommon use of the muscle. For example, eccentric contractions employ fewer active motor units to generate higher forces. In such case, the over-extended muscle units experience excessive tension during lengthening. The excessive tension may cause microscopic damages to the contractile element of the muscle, centering on what appears to be random disruptions of the Z-Iines. When the muscle is damaged, the affected person may experience a delayed onset muscle soreness, characterized by pain, weakness and a limited range of motion. The pain is most intense for about 1 to 2 days after the muscle injury and the weakness and limited range of motion can last for a week or more. If a minor strain of the skeletal muscles is treated inappropriately, a more serious injury can occur.
There are three classifications of muscle strains, based on the severity of the injury and the nature of the hematoma: (1) mild, (first degree) strain; a tear of a few muscle fibers; minor swelling and discomfort with no or only minimal loss of strength and restriction of movement; (2) moderate, (second degree) strain; a greater damage of muscle fibers with a clear loss of strength, and; (3) severe (third degree) strain; a tear extending across the whole muscle belly, resulting in a total loss of muscle function.
Tearing of the intramuscular blood vessels during muscle strain can often result in a large hematoma. Two different types of hematomas occur in the injured muscle: intramuscular and intermuscular hematomas. The first type, intramuscular hematomas, is limited in size by the intact muscle fascia. There, the extravasation of blood increases the intramuscular pressure, compressing and limiting the size of the hematoma. Such type of hematoma causes pain and loss of function of the muscle. The second type, intermuscular hematomas, develops when the muscle fascia is ruptured and extravasated blood spreads into the intermuscular spaces without significantly increasing the pressure within the muscle. This type of hematoma may not cause significant pain if the pressure within the muscle does not increase.
For treatments of strain injuries, it is critical that the injured muscle be immobilized, especially during the first two to three days after the injury, since mobilization of the injured muscles immediately after the injury often causes re-rupturing at the original injury site. A re-rupturing may lead to more severe injuries, delayed healing and scarring of tissues. Jarvinen et al., Curr Opin Rheumatol, vol 12:155-161 (2000).
Re-rupturing of the damaged site may be avoided by immobilizing the injured muscle, preferably immediately after the injury. Immobilization allows the newly formed granulation tissue to reach sufficient tensile strength to withstand the forces created by contracting muscle.
A known method for immobilization of an injured/strained muscle requires use of a physical restraint or cast. For example, a cervical collar can be used to immobilize an injured cervical flexor or extensor. However, the use of a restraint is often cumbersome and uncomfortable. Moreover, for injuries of certain muscle groups, it is not practical or possible to use a physical restraint. For example, it is very difficult to immobilize a strained upper trapezius or gluteus maximus muscle with a restraint.
Botulinum Toxin
The anaerobic, gram positive bacterium Clostridium botulinum produces a potent polypeptide neurotoxin, botulinum toxin, which causes a neuroparalytic illness in humans and animals referred to as botulism. The spores of Clostridium botulinum are found in soil and can grow in improperly sterilized and sealed food containers of home based canneries, which are the cause of many of the cases of botulism. The effects of botulism typically appear 18 to 36 hours after eating the foodstuffs infected with a Clostridium botulinum culture or spores. The botulinum toxin can apparently pass unattenuated through the lining of the gut and attack peripheral motor neurons. Symptoms of botulinum toxin intoxication can progress from difficulty walking, swallowing, and speaking to paralysis of the respiratory muscles and death.
Botulinum toxin type A (xe2x80x9cBoNT/Axe2x80x9d) is the most lethal natural biological neurotoxin known to man. About 50 picograms of botulinum toxin (purified neurotoxin complex) serotype A is a LD50 in mice. One unit (U) of botulinum toxin is defined as the LD50 upon intraperitoneal injection into female Swiss Webster mice weighing 18-20 grams each. Seven immunologically distinct botulinum neurotoxins have been characterized, these being respectively botulinum neurotoxin serotypes A, B, C1, D, E, F and G each of which is distinguished by neutralization with serotype-specific antibodies. The different serotypes of botulinum toxin vary in the animal species that they affect and in the severity and duration of the paralysis they evoke. For example, it has been determined that BoNt/A is 500 times more potent, as measured by the rate of paralysis produced in the rat, than is botulinum toxin serotype B (BoNT/B). Additionally, BoNt/B has been determined to be non-toxic in primates at a dose of 480 U/kg which is about 12 times the primate LD50 for BoNt/A. Botulinum toxin apparently binds with high affinity to cholinergic motor neurons, is translocated into the neuron and blocks the release of acetylcholine.
Botulinum toxins have been used in clinical settings for the treatment of neuromuscular disorders characterized by hyperactive skeletal muscles. BoNt/A has been approved by the U.S. Food and Drug Administration for the treatment of blepharospasm, strabismus and hemifacial spasm. Non-serotype A botulinum toxin serotypes apparently have a lower potency and/or a shorter duration of activity as compared to BoNt/A. Clinical effects of intramuscular of a botulinum toxin, such as BoNt/A, can be noted in a matter of hours. Thus, it is important to note that most if not all of the botulinum toxins can, upon intramuscular injection, produce significant muscle paralysis within one day of the injection, as measured, for example, by the mouse Digit Abduction Score (DAS). Aoki K. R., Preclinical Update on BOTOX (Botulinum Toxin Type A)-Purified Neurotoxin Complex Relative to Other Botulinum Toxin Preparations, Eur J. Neur 1999, 6 (suppl 4):S3-S10. The typical duration of symptomatic relief from a single intramuscular injection of BoNt/A averages about three months. Botulinum toxins, including botulinum toxin type A, with reduced periods of in vivo biological activity are set forth in co-pending U.S. patent application Ser. No. 09/620840, which application is incorporated herein by reference in its entirety.
Although all the botulinum toxins serotypes apparently inhibit release of the neurotransmitter acetylcholine at the neuromuscular junction, they do so by affecting different neurosecretory proteins and/or cleaving these proteins at different sites. For example, botulinum serotypes A and E both cleave the 25 kiloDalton (kD) synaptosomal associated protein (SNAP-25), but they target different amino acid sequences within this protein. BoNT/B, D, F and G act on vesicle-associated protein (VAMP, also called synaptobrevin), with each serotype cleaving the protein at a different site. Finally, botulinum toxin serotype C1 (BoNT/C1) has been shown to cleave both syntaxin and SNAP-25. These differences in mechanism of action may affect the relative potency and/or duration of action of the various botulinum toxin serotypes.
Regardless of serotype, the molecular mechanism of toxin intoxication appears to be similar and to involve at least three steps or stages. In the first step of the process, the toxin binds with high affinity to the presynaptic membrane of the target neuron through a specific interaction between the H chain and a cell surface receptor; the receptor is thought to be different for each serotype of botulinum toxin and for tetanus toxin. The carboxyl end segment of the H chain, Hc, appears to be important for targeting of the toxin to the cell surface.
In the second step, the toxin crosses the plasma membrane of the poisoned cell. The toxin is first engulfed by the cell through receptor-mediated endocytosis, and an endosome containing the toxin is formed. The toxin then escapes the endosome into the cytoplasm of the cell. This last step is thought to be mediated by the amino end segment of the H chain, HN, which triggers a conformational change of the toxin in response to a pH of about 5.5 or lower. Endosomes are known to possess a proton pump which decreases intra endosomal pH. The conformational shift exposes hydrophobic residues in the toxin, which permits the toxin to embed itself in the endosomal membrane. The toxin then translocates through the endosomal membrane into the cytosol.
The last step of the mechanism of botulinum toxin activity appears to involve cleavage of the critical intracellular exocytosis proteins by the L chain. The entire toxic activity of botulinum and tetanus toxins is contained in the L chain of the holotoxin; the L chain is a zinc (Zn++) endopeptidase which selectively cleaves proteins essential for recognition and docking of neurotransmitter-containing vesicles with the cytoplasmic surface of the plasma membrane, and fusion of the vesicles with the plasma membrane. Tetanus neurotoxin, botulinum toxin/B/D,/F, and/G cause degradation of synaptobrevin (also called vesicle-associated membrane protein (VAMP)), a synaptosomal membrane protein. Most of the VAMP present at the cytosolic surface of the synaptic vesicle is removed as a result of any one of these cleavage events. Each toxin specifically cleaves a different bond.
The molecular weight of the botulinum toxin protein molecule, for all seven of the known botulinum toxin serotypes, is about 150 kD. Interestingly, the botulinum toxins are released by Clostridial bacterium as complexes comprising the 150 kD botulinum toxin protein molecule along with associated non-toxin proteins. Thus, the BoNt/A complex can be produced by Clostridial bacterium as 900 kD, 500 kD and 300 kD forms. BoNT/B and C1 are apparently produced as only a 500 kD complex. BoNT/D is produced as both 300 kD and 500 kD complexes. Finally, BoNT/E and F are produced as only approximately 300 kD complexes. The complexes (i.e. molecular weight greater than about 150 kD) are believed to contain a non-toxin hemaglutinin protein and a non-toxin and non-toxic nonhemaglutinin protein. These two non-toxin proteins (which along with the botulinum toxin molecule comprise the relevant neurotoxin complex) may act to provide stability against denaturation to the botulinum toxin molecule and protection against digestive acids when toxin is ingested. Additionally, it is possible that the larger (greater than about 150 kD molecular weight) botulinum toxin complexes may result in a slower rate of diffusion of the botulinum toxin away from a site of intramuscular injection of a botulinum toxin complex.
In vitro studies have indicated that botulinum toxin inhibits potassium cation induced release of both acetylcholine and norepinephrine from primary cell cultures of brainstem tissue. Additionally, it has been reported that botulinum toxin inhibits the evoked release of both glycine and glutamate in primary cultures of spinal cord neurons and that in brain synaptosome preparations botulinum toxin inhibits the release of each of the neurotransmitters acetylcholine, dopamine, norepinephrine, CGRP and glutamate.
BoNt/A can be obtained by establishing and growing cultures of Clostridium botulinum in a fermenter and then harvesting and purifying the fermented mixture in accordance with known procedures. All the botulinum toxin serotypes are initially synthesized as inactive single chain proteins which must be cleaved or nicked by proteases to become neuroactive. The bacterial strains that make botulinum toxin serotypes A and G possess endogenous proteases and serotypes A and G can therefore be recovered from bacterial cultures in predominantly their active form. In contrast, botulinum toxin serotypes C1, D and E are synthesized by nonproteolytic strains and are therefore typically unactivated when recovered from culture. Serotypes B and F are produced by both proteolytic and nonproteolytic strains and therefore can be recovered in either the active or inactive form. However, even the proteolytic strains that produce, for example, the BoNt/B serotype only cleave a portion of the toxin produced. The exact proportion of nicked to unnicked molecules depends on the length of incubation and the temperature of the culture. Therefore, a certain percentage of any preparation of, for example, the BoNt/B toxin is likely to be inactive, possibly accounting for the known significantly lower potency of BoNt/B as compared to BoNt/A. The presence of inactive botulinum toxin molecules in a clinical preparation will contribute to the overall protein load of the preparation, which has been linked to increased antigenicity, without contributing to its clinical efficacy. Additionally, it is known that BoNt/B has, upon intramuscular injection, a shorter duration of activity and is also less potent than BoNt/A at the same dose level.
It has been reported that BoNt/A has been used in clinical settings as follows:
(1) about 75-125 units of BOTOX(copyright)1 per intramuscular injection (multiple muscles) to treat cervical dystonia;
(2) 5-10 units of BOTOX(copyright) per intramuscular injection to treat glabellar lines (brow furrows) (5 units injected intramuscularly into the procerus muscle and 10 units injected intramuscularly into each corrugator supercilii muscle);
(3) about 30-80 units of BOTOX(copyright) to treat constipation by intrasphincter injection of the puborectalis muscle;
(4) about 1-5 units per muscle of intramuscularly injected BOTOX(copyright) to treat blepharospasm by injecting the lateral pre-tarsal orbicularis oculi muscle of the upper lid and the lateral pre-tarsal orbicularis oculi of the lower lid.
(5) to treat strabismus, extraocular muscles have been injected intramuscularly with between about 1-5 units of BOTOX(copyright), the amount injected varying based upon both the size of the muscle to be injected and the extent of muscle paralysis desired (i.e. amount of diopter correction desired).
(6) to treat upper limb spasticity following stroke by intramuscular injections of BOTOX(copyright) into five different upper limb flexor muscles, as follows:
(a) flexor digitorum profundus: 7.5 U to 30 U
(b) flexor digitorum sublimus: 7.5 U to 30 U
(c) flexor carpi ulnaris: 10 U to 40 U
(d) flexor carpi radialis: 15 U to 60 U
(e) biceps brachii: 50 U to 200 U. Each of the five indicated muscles has been injected at the same treatment session, so that the patient receives from 90 U to 360 U of upper limb flexor muscle BOTOX(copyright) by intramuscular injection at each treatment session.
The success of BoNt/A to treat a variety of clinical conditions has led to interest in other botulinum toxin serotypes. A study of two commercially available BoNT/A preparations (BOTOX(copyright) and Dysport(copyright)) and preparations of BoNT/B and F (both obtained from Wako Chemicals, Japan) has been carried out to determine the preclinical local muscle weakening efficacy, safety and antigenic potential. Botulinum toxin preparations were injected into the head of the right gastrocnemius muscle (0.5 to 200.0 units/kg) and muscle weakness was assessed using the mouse digit abduction scoring assay (DAS). ED50 values were calculated from dose response curves. Additional mice were given intramuscular injections to determine LD50 doses. The therapeutic index was calculated as LD50/ED50. Separate groups of mice received hind limb injections of BOTOX(copyright) (5.0 to 10.0 units/kg) or BoNt/B (50.0 to 400.0 units/kg), and were tested for muscle weakness and increased water consumption, the later being a putative model for dry mouth. Antigenic potential was assessed by monthly intramuscular injections in rabbits (2.0 or 8.7 Units/kg for BoNt/B or 3.0 Units/kg for BOTOX(copyright)). Peak muscle weakness and duration were dose related for all serotypes. DAS ED50 values (units/kg) were as follows: BOTOX(copyright): 6.7, Dysport(copyright): 24.7, BoNt/B: 11.8 to 244.0, BoNT/F: 4.3. BOTOX(copyright) had a longer duration of action than BoNt/B or BoNt/F. Therapeutic index values were as follows: BOTOX(copyright): 10.5, Dysport(copyright): 6.3, BoNt/B: 4.8. Water consumption was greater in mice injected with BoNt/B than with BOTOX(copyright), although BoNt/B was less effective at weakening muscles. After four months of injections 2 of 4 (where treated with 1.5 ng/kg) and 4 of 4 (where treated with 6.5 ng/kg) rabbits developed antibodies against BoNt/B. In a separate study, 0 of 9 BOTOX(copyright) treated rabbits demonstrated antibodies against BoNt/A. DAS results indicate relative peak potencies of BoNt/A being equal to BoNt/F, and BoNt/F being greater than BoNt/B. With regard to duration of effect, BoNt/A was greater than BoNt/B, and BoNt/B duration of effect was greater than BoNt/F. As shown by the therapeutic index values, the two commercial preparations of BoNt/A (BOTOX(copyright) and Dysport(copyright)) are different. The increased water consumption behavior observed following hind limb injection of BoNt/B indicates that clinically significant amounts of this serotype entered the murine systemic circulation. The results also indicate that in order to achieve efficacy comparable to BoNt/A, it is necessary to increase doses of the other serotypes examined. Increased dosage can comprise safety. Furthermore, in rabbits, serotype B was more antigenic than was BOTOX(copyright), possibly because of the higher protein load injected to achieve an effective dose of BoNt/B.
The tetanus neurotoxin acts mainly in the central nervous system, while botulinum neurotoxin acts at the neuromuscular junction; both act by inhibiting acetylcholine release from the axon of the affected neuron into the synapse, resulting in paralysis. The effect of intoxication on the affected neuron is long-lasting and until recently has been thought to be irreversible. The tetanus neurotoxin is known to exist in one immunologically distinct serotype.
Acetylcholine
Typically only a single type of small molecule neurotransmitter is released by each type of neuron in the mammalian nervous system. The neurotransmitter acetylcholine is secreted by neurons in many areas of the brain, but specifically by the large pyramidal cells of the motor cortex, by several different neurons in the basal ganglia, by the motor neurons that innervate the skeletal muscles, by the preganglionic neurons of the autonomic nervous system (both sympathetic and parasympathetic), by the postganglionic neurons of the parasympathetic nervous system, and by some of the postganglionic neurons of the sympathetic nervous system. Essentially, only the postganglionic sympathetic nerve fibers to the sweat glands, the piloerector muscles and a few blood vessels are cholinergic and most of the postganglionic neurons of the sympathetic nervous system release the neurotransmitter norepinephrine. In most instances acetylcholine has an excitatory effect. However, acetylcholine is known to have inhibitory effects at some of the peripheral parasympathetic nerve endings, such as inhibition of the heart by the vagal nerve.
The efferent signals of the autonomic nervous system are transmitted to the body through either the sympathetic nervous system or the parasympathetic nervous system. The preganglionic neurons of the sympathetic nervous system extend from preganglionic sympathetic neuron cell bodies located in the intermediolateral horn of the spinal cord. The preganglionic sympathetic nerve fibers, extending from the cell body, synapse with postganglionic neurons located in either a paravertebral sympathetic ganglion or in a prevertebral ganglion. Since, the preganglionic neurons of both the sympathetic and parasympathetic nervous system are cholinergic, application of acetylcholine to the ganglia will excite both sympathetic and parasympathetic postganglionic neurons.
Acetylcholine activates two types of receptors, muscarinic and nicotinic receptors. The muscarinic receptors are found in all effector cells stimulated by the postganglionic neurons of the parasympathetic nervous system, as well as in those stimulated by the postganglionic cholinergic neurons of the sympathetic nervous system. The nicotinic receptors are found in the synapses between the preganglionic and postganglionic neurons of both the sympathetic and parasympathetic. The nicotinic receptors are also present in many membranes of skeletal muscle fibers at the neuromuscular junction.
Acetylcholine is released from cholinergic neurons when small, clear, intracellular vesicles fuse with the presynaptic neuronal cell membrane. A wide variety of non-neuronal secretory cells, such as, adrenal medulla (as well as the PC12 cell line) and pancreatic islet cells release catecholamines and insulin, respectively, from large dense-core vesicles. The PC12 cell line is a clone of rat pheochromocytoma cells extensively used as a tissue culture model for studies of sympathoadrenal development. Botulinum toxin inhibits the release of both types of compounds from both types of cells in vitro, permeabilized (as by electroporation) or by direct injection of the toxin into the denervated cell. Botulinum toxin is also known to block release of the neurotransmitter glutamate from cortical synaptosomes cell cultures.
A neuromuscular junction is formed in skeletal muscle by the proximity of axons to muscle cells. A signal transmitted through the nervous system results in an action potential at the terminal axon, with activation of ion channels and resulting release of the neurotransmitter acetylcholine from intraneuronal synaptic vesicles, for example at the motor endplate of the neuromuscular junction. The acetylcholine crosses the extracellular space to bind with acetylcholine receptor proteins on the surface of the muscle end plate. Once sufficient binding has occurred, an action potential of the muscle cell causes specific membrane ion channel changes, resulting in muscle cell contraction. The acetylcholine is then released from the muscle cells and metabolized by cholinesterases in the extracellular space. The metabolites are recycled back into the terminal axon for reprocessing into further acetylcholine.
As discussed above, the present methods of treating injured muscles are still inadequate. There is a need to have improved methods of treating injured muscles.
In accordance with the present invention, an effective method for treating an injured muscle includes the step of in vivo, local administration of a therapeutically effective amount of a neurotoxin into or to the vicinity of the injured muscle. The neurotoxin functions to provide a temporary chemodenervation of the injured muscle and to reduce the muscle""s contractions. An objective of the present invention is to facilitate healing and a speedy return to function of an injured muscle. The injured muscle may be, for example, a strained muscle. In one embodiment, the neurotoxin is administered intramuscularly or subcutaneously. In another embodiment, the step of administering a neurotoxin is preceded by and/or followed by physical therapy and/or surgery.
Further in accordance with the invention, the step of administering the neurotoxin is immediately after the muscle is injured, or is as soon thereafter as is practical. In one embodiment, the neurotoxin is effective to immobilize or to substantially immobilize the injured muscle during at least phase 1 and/or phase 2 of the repair process of the injured muscle.
In accordance with the invention, the neurotoxin can include a targeting component, a therapeutic component and a translocation component. The targeting component can bind to a presynaptic motor neuron. In one embodiment, the targeting component can comprise a carboxyl end fragment of a heavy chain of a butyricum toxin, a tetani toxin, or of a botulinum toxin type A, B, C1, D, E, F, G or a variant thereof. The therapeutic component can interfere with or modulate the release of a neurotransmitter from a neuron or its processes. In one embodiment, the therapeutic component comprises a light chain of a butyricum toxin, a tetani toxin, or of a botulinum toxin type A, B, C1, D, E, F, G or a variant thereof. The translocation component can facilitate the transfer of at least a part of the neurotoxin, for example the therapeutic component, into the cytoplasm of the target cell. In one embodiment, the translocation component can comprise an amino end fragment of a heavy chain of a butyricum toxin, a tetani toxin, or of a botulinum toxin type A, B, C1, D, E, F, G or variants thereof.
Still further in accordance with the invention, the neurotoxin is a botulinum toxin type A, B, E and/or F. In a preferred embodiment, the neurotoxin used to treat an injured muscle is botulinum toxin type A. In fact, the use of botulinum toxin type A is preferred because of its commercial availability, known clinical uses, and successful application to treat muscle injury according to the present invention, as disclosed herein. Use of from about 0.1 U/kg to about 30 U/kg of a botulinum toxin type A and from about 1 U/kg to about 150 U/kg of a botulinum toxin type B is within the scope of a method practiced according to the present disclosed invention. With regard to the other botulinum toxin serotypes (including toxin types E and F) the U/kg dosage to be used is within the range of about 0.1 U/kg to about 150 U/kg, as set forth herein.
Still further in accordance with the invention, the neurotoxin can be recombinantly produced.
A detailed embodiment of the present invention is a method for treating (as by promoting the healing of) an injured muscle by in vivo, local administration of a therapeutically effective amount of a botulinum toxin to an injured muscle, thereby treating the injured muscle. The botulinum toxin can be botulinum toxin type A. Significantly, the present invention also encompasses a method for treating pain associated with an injured muscle by in vivo, local administration of a therapeutically effective amount of a botulinum toxin to an injured muscle, thereby reducing the pain associated with an injured muscle.
Each and every feature described herein, and each and every combination of two or more of such features, is included within the scope of the present invention provided that the features included in such a combination are not mutually inconsistent.
Definitions
The following definitions are provided and apply herein. xe2x80x9cAboutxe2x80x9d means approximately or nearly and in the context of a numerical value or range set forth herein means xc2x110% of the numerical value or range recited or claimed.
xe2x80x9cHeavy chainxe2x80x9d means the heavy chain of a clostridial neurotoxin. It preferably has a molecular weight of about 100 kDa and may be referred to herein as H chain or as H.
xe2x80x9cHNxe2x80x9d means a fragment (preferably having a molecular weight of about 50 kDa) derived from the H chain of a Clostridial neurotoxin which is approximately equivalent to the amino terminal segment of the H chain, or the portion corresponding to that fragment in the intact in the H chain. It is believed to contain the portion of the natural or wild type clostridial neurotoxin involved in the translocation of the L chain across an intracellular endosomal membrane.
xe2x80x9cHcxe2x80x9d means a fragment (about 50 kDa) derived from the H chain of a clostridial neurotoxin which is approximately equivalent to the carboxyl terminal segment of the H chain, or the portion corresponding to that fragment in the intact H chain. It is believed to be immunogenic and to contain the portion of the natural or wild type Clostridial neurotoxin involved in high affinity, presynaptic binding to motor neurons.
xe2x80x9cInjured musclexe2x80x9d includes a strained, torn or pulled muscle, as well as a muscle with a contusion (bruise), laceration, ischemia or rupture.
xe2x80x9cLight chainxe2x80x9d means the light chain of a clostridial neurotoxin. It preferably has a molecular weight of about 50 kDa, and can be referred to as L chain, L or as the proteolytic domain (amino acid sequence) of a clostridial neurotoxin. The light chain is believed to be effective as an inhibitor of neurotransmitter release when it is released into a cytoplasm of a target cell.
xe2x80x9cLocal administrationxe2x80x9d means direct administration of a pharmaceutical at or to the vicinity of a site on or within an animal body, at which site a biological effect of the pharmaceutical is desired. Local administration excludes systemic routes of administration, such as intravenous or oral administration.
xe2x80x9cNeurotoxinxe2x80x9d means a chemical entity that is capable of interfering with or modulating at least one function of a neuron. The xe2x80x9cneurotoxinxe2x80x9d can be naturally occurring or man-made. Furthermore, the xe2x80x9cneurotoxinxe2x80x9d can be a small molecule, a large molecule, a polypeptide, a conjugated-polypeptide or mixtures thereof.
xe2x80x9cVariantxe2x80x9d means a chemical entity which is slightly different from a parent chemical entity but which still has a biological effect. The biological effect of the variant may be substantially the same or better than that of the parent. For example, a variant light chain of a botulinum toxin having at least one amino acid replaced, modified, deleted or added, may have the same or better ability to prevent the release of neurotransmitter vesicles. Additionally, the biological effect of a variant may be decreased. For example, a variant light chain of a botulinum toxin type A having a leucine-based motif removed may have a shorter biological persistence than that of the parent (or native) botulinum toxin type A light chain.
In a broad embodiment, an effective method for treating an injured muscle according to the present invention can include the step of locally administering a therapeutically effective amount of a neurotoxin into an injured muscle. Preferably, the injured muscle is a strained muscle.
A strain injury of the skeletal muscle may be classified as a shearing injury. In shearing injury, not only the myofibers but also the mysial sheaths are torn. Almost immediately after the injury of the muscle, a repair process of muscle begins. The repair process of the shearing injury may be divided into three phases.
Phase 1 is the destruction phase, which is characterized by hematoma formation, myofiber necrosis, and inflammatory cell reaction. The site of rupture of an otherwise healthy muscle often occurs close to its distal myotendinous junction (MTJ) after a strain. The ruptured myofibers contract and a gap is formed between the stumps. Because skeletal muscle is richly vascularized, hemorrhage from the torn vessels is inescapable and the gap becomes filled with a hematoma, later replaced by scar tissue. In shearing injuries the mechanical force tears the entire myofiber, damaging the myofiber plasma membrane and leaving sarcoplasm open at the ends of the stumps. Because myofibers are very long, string-like cells, the necrosis initiated at this site extends all along the whole length of the ruptured myofiber. The blood vessels are also torn in shearing injuries; thus, blood-borne inflammatory cells gain immediate access to the injury site to induce an inflammation. Phase 1 persists for about 2 to 3 days following the injury.
Phase 2 is the repair phase, which consists of phagocycosis of the necrotized tissue, regeneration of the myofibers, production of connective tissue scar, and capillary ingrowth. The key step in the regeneration of injured muscle tissue is the vascularization of the injured area. The restoration of vascular supply is necessary for the regeneration of an injured muscle. The new capillaries sprout from surviving trunks of blood vessels and pierce toward the center of an injured area. These new capillaries help provide adequate oxygen supply to the regenerating area.
Phase 3 is the remodeling phase, which consists of maturation of the regenerated myofibers, contraction and reorganization of the scar tissue, and restoration of the functional capacity of the repaired muscle. Phase 2 (repair) and 3 (remodeling) often occur simultaneously and persists for about 2 days to about six weeks following phase 1.
In one embodiment of the present invention, the neurotoxin is locally administered, preferably intramuscularly, to immobilize the injured muscle to facilitate healing. Local administration of a neurotoxin according to the present disclosed invention can also reduce the pain experienced due to a muscle injury. Preferably, the administration of the neurotoxin is immediately at the time of injury or closely thereafter. In one preferred embodiment, the neurotoxin is effective to immobilize the injured muscle during the destruction phase (phase 1) to prevent re-rupturing of the muscle.
Without wishing to limit the invention to any particular theory or mechanism of operation, it is believed that mobilization during the repair and/or remodeling phases is beneficial in that such mobilization induces more rapid and intensive capillary ingrowth to the injured area, as well as better muscle fiber regeneration and orientation. Therefore, in one embodiment, the immobilizing effect of the neurotoxin is absent during the repair phase (phase 2) and/or remodeling phase (phase 3). In a more preferred embodiment, the neurotoxin is administered and is effective to immobilize the injured muscle during phase 1, but not during phases 2 and 3 of the repair process. For example, if the neurotoxin is injected, preferably intramuscularly, immediately to the muscle following an injury, it is preferable that the neurotoxin immobilizes the injured muscle for about 3 days after the time of administration. Alternatively, the neurotoxin can have its immobilization effect only up to the point where the patient experiences little or no pain in the use of the injured muscle in basic movements. When this critical point is reached, the patient should be encouraged to start active, progressive mobilization.
In another embodiment of the present invention, the neurotoxin is effective to immobilize the injured muscle for all of the phase 1-3 periods and for a subsequent muscle injury recovery period thereafter.
Neurotoxins, such as certain of the botulinum toxins, which can require from less than about one day to about seven days to exhibit significant clinical muscle paralysis effect and/or where the muscle paralysis effect is sustained post injection for a period of several months, are within the scope of the present invention, as such neurotoxins can be used to treat relatively serious or long lasting muscle injuries or where a long period of muscle immobilization is indicated for proper healing.
In a broad embodiment, the neurotoxin is a neuromuscular blocking agent. Table 1 shows a non-limiting list of neuromuscular blocking agents and their potential site of actions. In an embodiment, neuromuscular blocking agents having the ability to immobilize muscles, preferably injured muscles, for at least about 5 days, and preferably for at least about 3 days are administered to treat injured muscles. In a preferred embodiment of the present invention, the neurotoxin is a botulinum toxin because of the known uses and clinical safety of a botulinum toxin, such as botulinum toxin type E to treat muscle disorders, such as muscle spasms. In a particularly preferred embodiment of the present invention, especially for severe, or third degree muscle injuries, the locally administered botulinum toxin is a botulinum toxin type E. Botulinum toxin type A can also be used in both these embodiments.
In a broad embodiment, the neurotoxin can comprise a targeting component, a therapeutic component and a translocation component. The targeting component can bind to a presynaptic motor neuron. In one embodiment, the targeting component can comprise a carboxyl end fragment of a heavy chain of a butyricum toxin, a tetani toxin, a botulinum toxin type A, B, C1D, E, F, G or a variant thereof. In a preferred embodiment, the targeting component can include a carboxyl end fragment of a botulinum toxin type A.
The therapeutic component can substantially interfere with or modulate the release of neurotransmitters from a cell or its processes. In one embodiment, the therapeutic component comprises a light chain of a butyricum toxin, a tetani toxin, a botulinum toxin type A, B, C1, D, E, F, G or a variant thereof. In a preferred embodiment, the therapeutic component may include a light chain of a botulinum toxin type which has a short biological persistence, for example less than about 5 days, preferably less than about 3 days. Preferably, such light chain can be a light chain of a botulinum toxin type E or F. Alternately, the light chain can be a light chain of a botulinum toxin type A.
The translocation component can facilitate the transfer of at least a part of the neurotoxin, for example the therapeutic component into the cytoplasm of the target cell. In one embodiment, the translocation component comprises an amino end fragment of a heavy chain of a butyricum toxin, a tetani toxin, a botulinum toxin type A, B, C1, D, E, F, G or variants thereof. In a preferred embodiment, the translocation component comprises an amino end fragment of a heavy chain of a botulinum toxin type A.
In one embodiment, the targeting component comprises a carboxyl end fragment of a heavy chain of a botulinum toxin type E or F, the therapeutic component comprises a light chain of a botulinum toxin type E or F and the translocation component comprises an amine end fragment of a heavy chain of a botulinum toxin type E or F. In a preferred embodiment, the neurotoxin comprises a botulinum toxin type E. In another preferred embodiment, the neurotoxin comprises a botulinum toxin type F. In yet another embodiment, the neurotoxin comprises a mixture of botulinum toxin type E and F.
In one embodiment, the targeting component comprises a carboxyl end fragment of a heavy chain of a botulinum toxin type A, the therapeutic component comprises a light chain of a botulinum toxin type A and the translocation component comprises an amine end fragment of a heavy chain of a botulinum toxin type A. In a preferred embodiment, the neurotoxin of the present invention comprises a botulinum toxin type A. A suitable botulinum toxin type A to use herein is BOTOX(copyright) (Allergan, Inc., Irvine, Calif.)
Although the neurotoxins of the present invention treats injured muscles by immobilizing them, in one embodiment, the neurotoxin may also be administered to injured muscles to reduce pain and/or spasm. In another embodiment, the neurotoxin is able to immobilize the injured muscle and to reduce pain associated with that injured muscle. In a preferred embodiment, a neurotoxin, for example a botulinum toxin type E, or most preferably type A, is administered to a strained muscle to immobilize the muscle and/or to reduce pain associated with that muscle.
Of course, an ordinarily skilled medical provider can determine the appropriate dose and frequency of administration(s) to achieve an optimum clinical result. That is, one of ordinary skill in medicine would be able to administer the appropriate amount of the neuromuscular blocking agent at the appropriate time(s) to effectively immobilize the injured muscle(s). The dose of the neurotoxin to be administered depends upon a variety of factors, including the size of the muscle, the severity of the muscle injury. In a preferred embodiment, the dose of the neurotoxin administered immobilizes the injured muscle(s) for no longer than the duration of phase 1 of the repair process. In the various methods of the present invention, from about 0.1 U/kg to about 15 U/kg, of botulinum toxin type A can be administered to the injured muscle. Preferably, about 1 U/kg to about 20 U/kg of botulinum toxin type A may be administered to the injured muscle. Use of from about 0.1 U/kg to about 30 U/kg of a botulinum toxin type A and from about 1 U/kg to about 150 U/kg of a botulinum toxin type B is within the scope of a method practiced according to the present disclosed invention. With regard to the other botulinum toxin serotypes (including toxin types E and F) the U/kg dosage to be used is within the range of about 0.1 U/kg to about 150 U/kg, as set forth herein.
Although intramuscular injection is the preferred route of administration, other routes of local administration are available, such as subcutaneous administration.
In another broad embodiment, the method of treating injured muscle according to this invention further includes other steps described below. These other steps may be taken prior to, in conjunction with or following the step of administering a neurotoxin, preferably to the injured muscle. For example, the present recommended treatment for strained muscle includes resting, icing, compression and elevating. These four steps (or procedures) have the same objective. They minimize bleeding from ruptured blood vessels to rupture site. This will prevent the formation of a large hematoma, which has a direct impact on the size of scar tissue at the end of the regeneration. A small hematoma and the limitation of interstitial edema accumulation on the rupture site also shorten the ischemic period in the granulation tissue, which in turn accelerates regeneration.
Other additional steps may be employed in the treatment of injured muscles. In one embodiment, the additional steps include an administration of nonsteroidal anti-inflammatory drugs (NSAIDs), therapeutic ultrasound, hyperbaric oxygen, and in severe injuries, surgery may also be employed. NSAIDs should be a part of early treatment and should be started immediately after the injury. Short-term use of NSAIDs in the early phase of healing decreases the inflammatory cell reaction, and has no adverse effects on tensile or contractile properties of injured muscle.
In another embodiment, the additional step includes the use of therapeutic ultrasound. Therapeutic ultrasound is widely recommended and used in the treatment of muscle strains. It is thought that therapeutic ultrasound promotes the proliferation phase of myoregeneration.
In another embodiment, the additional step includes the use of hyperbaric oxygen. It is known that hyperbaric oxygen therapy in rabbits during the early phase of the repair substantially improves the final outcome. It is believed that such hyperbaric oxygen therapy in other mammals, for example human beings, may be helpful, such as by speeding up muscle regeneration.
In another embodiment, the additional step includes surgical intervention. Surgical treatment of muscle injuries should be reserved for the most serious injuries, because in most cases conservative treatment results in a good outcome. Surgical treatment is indicated only in cases of (1) large intramuscular hematomas, (2) third-degree strains or tears of muscles with few or no agonise muscles, and (3) second-degree strains, if more than half of the muscle belly is torn.
In another broad aspect of this invention, recombinant techniques are used to produce at least one of the components of the neurotoxins. The technique includes steps of obtaining genetic materials from either DNA cloned from natural sources, or synthetic oligonucleotide sequences, which have codes for one of the components, for example the therapeutic, translocation and/or targeting component(s). The genetic constructs are incorporated into host cells for amplification by first fusing the genetic constructs with cloning vectors, such as phages or plasmids. Then the cloning vectors are inserted into hosts, preferably E. coli""s. Following the expressions of the recombinant genes in host cells, the resultant proteins can be isolated using conventional techniques. The protein expressed may comprise all three components of the neurotoxin. For example, the protein expressed may include a light chain of botulinum toxin type E (the therapeutic component), a heavy chain, preferably HN, of a botulinum toxin type B (the translocation component), and an Hc of botulinum toxin type A, which selectively binds to the motor neurons. In one embodiment, the protein expressed may include less than all three components of the neurotoxin. In such case, the components may be chemically joined using techniques known in the art.
There can be many advantages to producing these neurotoxins recombinantly. For example, production of neurotoxin from anaerobic Clostridium cultures is a cumbersome and time-consuming process including a multi-step purification protocol involving several protein precipitation steps and either prolonged and repeated crystallization of the toxin or several stages of column chromatography. Significantly, the high toxicity of the product dictates that the procedure must be performed under strict containment (BL-3). During the fermentation process, the folded single-chain neurotoxins are activated by endogenous Clostridial proteases through a process termed nicking. This involves the removal of approximately 10 amino acid residues from the single-chain to create the dichain form in which the two chains remain covalently linked through the intrachain disulfide bond.
The nicked neurotoxin is much more active than the unnicked form. The amount and precise location of nicking varies with the serotypes of the bacteria producing the toxin. The differences in single-chain neurotoxin activation and, hence, the yield of nicked toxin, are due to variations in the type and amounts of proteolytic activity produced by a given strain. For example, greater than 99% of Clostridial botulinum type A single-chain neurotoxin is activated by the Hall A Clostridial botulinum strain, whereas type B and E strains produce toxins with lower amounts of activation (0 to 75% depending upon the fermentation time). Thus, the high toxicity of the mature neurotoxin plays a major part in the commercial manufacture of neurotoxins as therapeutic neurotoxins.
The degree of activation of engineered Clostridial toxins is, therefore, an important consideration for manufacture of these materials. It would be a major advantage if neurotoxins such as botulinum toxin and tetanus toxin could be expressed, recombinantly, in high yield in rapidly-growing bacteria (such as heterologous E. coli cells) as relatively non-toxic single-chains (or single chains having reduced toxic activity) which are safe, easy to isolate and simple to convert to the fully-active form.
With safety being a prime concern, previous work has concentrated on the expression in E. coli and purification of individual H and L chains of tetanus and botulinum toxins; these isolated chains are, by themselves, non-toxic; see Li et al., Biochemistry 33:7014-7020 (1994); Zhou et al., Biochemistry 34:15175-15181 (1995), hereby incorporated by reference herein. Following the separate production of these peptide chains and under strictly controlled conditions the H and L subunits can be combined by oxidative disulphide linkage to form the neuroparalytic di-chains.